Mobile communication has been one of the most successful innovations in the 20th century. In recent years, the number of subscribers to mobile communication services has exceeded 4.5 billion and is growing fast. At the same time, new mobile communication technologies have been developed to satisfy the increasing needs and to provide more and better mobile communication applications and services. Some examples of such systems are Code Division Multiple Access 2000 (cdma2000) 1xEV-DO systems developed by 3GPP2, WCDMA, HSPA, and Long Term Evolution (LTE) systems developed by 3rd Generation Partnership Project (3GPP), and mobile WiMAX systems developed by the Institute of Electrical and Electronics Engineers (IEEE). As more and more people become users of mobile communication systems, and more and more services are provided over these systems, there is an increasing need of a mobile communication system with larger capacity, higher throughput, lower latency, and better reliability.
Millimeter waves are radio waves with wavelength in the range of 1 mm-10 mm, which corresponds to radio frequency of 30 GHz-300 GHz. Per definition by the International Telecommunications Union (ITU), these frequencies are also referred to as the Extremely High Frequency (EHF) band. These radio waves exhibit unique propagation characteristics. For example, compared with lower frequency radio waves, they suffer higher propagation loss, have poorer ability to penetrate objects, such as buildings, walls, foliage, and are more susceptible to atmosphere absorption, deflection and diffraction due to particles (e.g., rain drops) in the air. Alternatively, due to their smaller wave lengths, more antennas can be packed in a relative small area, thus enabling high-gain antenna in small form factor. In addition, due to the aforementioned deemed disadvantages, these radio waves have been less utilized than the lower frequency radio waves. This also presents unique opportunities for new businesses to acquire the spectrum in this band at a lower cost. The ITU defines frequencies in 3 GHz-30 GHz as Super High Frequency (SHF). However, some higher frequencies in the SHF band also exhibit similar behavior as radio waves in the EHF band (i.e., millimeter waves), such as large propagation loss and the possibility of implementing high-gain antennas in small form factor.
Vast amount of spectrum are available in the millimeter wave band. For example, the frequencies around 60 GHz, which are typically referred to as 60 GHz band, are available as unlicensed spectrum in most countries. In the United States, 7 GHz of spectrum around 60 GHz (57 GHz-64 GHz) is allocated for unlicensed use. On Oct. 16, 2003, the Federal Communications Commission (FCC) issued a Report and Order that allocated 12.9 GHz of spectrum for high-density fixed wireless services in the United States (71-76 GHz, 81-86 GHz, and 92-95 GHz excluding the 94.0-94.1 GHz for Federal Government use). The frequency allocation in 71-76 GHz, 81-86 GHz, and 92-95 GHz are collectively referred to as the E-band. It is the largest spectrum allocation ever by FCC—50 times larger than the entire cellular spectrum.